This application claims the priority of Korean Patent Application No. 2003-39349, filed on Jun. 18, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to a de-interlacing method of converting an interlaced video signal into a progressive video signal, an apparatus therefor, a video decoder, and a reproducing apparatus.
2. Description of the Related Art
In general, a video signal is implemented in an interlaced or progressive format. An interlaced video signal comprises a plurality of fields. A progressive video signal comprises a plurality of frames. One frame can be constructed by alternately inserting one type fields between the other type fields. In comparison with the progressive video signal, the interlaced video signal shows a high quality image with small data size. However, processing for the interlaced video signal is relatively complicated because the interlaced video signal has two types of fields used to display a single image.
On the other hand, when the interlaced video signal is input to a reproducing apparatus, such as a TV, capable of processing the progressive video signal, the interlaced video signal must be converted into the progressive video signal. Such format conversion is called a de-interlacing process, or interlaced-to-progressive conversion (IPC).
The de-interlacing process involves an interpolation process for converting fields of the interlaced video signal into a frame. The interpolation process is mainly classified into a temporal interpolation process and a spatial interpolation process. The temporal interpolation process utilizes an average pixel value of two temporally adjacent pixels. The spatial interpolation process utilizes an average pixel value of two spatially adjacent pixels. In general, the spatial interpolation process is performed under an assumption that spatially adjacent pixels have similar pixel values. As seen in an actual image, pixels near edges, or edge lines, such as a contour of an object, a boundary between an object and background, or a boundary between objects have similar pixel values. However, pixels at both sides of the edge have greatly different pixel values, although the pixels are spatially adjacent to each other. Therefore, if the interpolation process is performed based on only spatial adjacency without consideration of the edges, or the edge direction, the pixel values obtained by the interpolation process will have great errors. It is very important to accurately determine the edge directions in order to improve interpolation quality and reduce interpolation errors.
In a de-interlacing process in the prior art, edge directions are detected in only a limited number of directions, particularly, a vertical direction (90°) and near-vertical directions, and an interpolation process is performed on the detected edge directions. In this case, the edge directions in the vertical and near-vertical directions can be relatively accurately detected. Therefore, a frame obtained by performing the interpolation process on fields having the edges located in the vertical and near-vertical directions has somewhat high quality of image. However, since edges are far away from each other in the horizontal direction and near-horizontal directions, it is relatively difficult to detect the edge directions. Therefore, the frame obtained by performing the interpolation process on fields having the edges located in the horizontal direction and near-horizontal directions has low quality of image due to inaccurate detection of the edge directions. In particular, artifacts due to edges in the near-horizontal directions are more unpleasant to the eye than those in the near-vertical directions.
More particularly, in a conventional method of determining an edge direction, a difference value between pixels in a predetermined number of upper and lower horizontal pixel lines located above and below a to-be-interpolated pixel out of pixels in a field is obtained. Next, if the difference value is less than a predetermined threshold value, the corresponding direction is determined to be an edge direction. However, if the conventional method is applied to determine an edge in near-horizontal directions, an erroneous result may be obtained due to weak pixel correlation. Although a large number of pixels may be used to increase the pixel correlation, errors in the edge detection and calculation amount may increase.